National Aeronautics and Space Administration

Introduction

The recommended tool for producing phase-binned spectra is fasebin. Fasebin handles the extraction, barycenter correction, and phase-binning of input RXTE data, eliminating the need to run separate tools for these various functions. It produces a single FITS file in the OGIP Type 2 spectral format: each row in the output file is a separate spectrum associated with a given phase bin. Other tools in the fasebin suite can then be used to subtract persistent emission (fbsub), combine phase-bins (fbfsum), and produce a "counts-per-phase-bin" histogram (fbssum). Examples of each will be shown below.

Data files you will need

To run fasebin you will need to have the following:

Running fasebin

Combining fasebin files from different Orbit days

To combine data of the same source and configuration taken over multiple Orbit days:

Analyzing fasebin spectra in xspec

Phase-binned spectral files from any of the fasebin tools may be read directly into xspec 10.0 or higher. (Earlier versions of XSPEC do not support OGIP Type 2 Spectral FITS files.) The syntax for reading Type 2 spectral files in xspec is:

 XSPEC>  data alldays.pha{10}

This will read the 10th spectrum (ie., the tenth row) of your phase-binned .pha file; to display more than one spectrum at a time, use the "data 1", "data 2" syntax in xspec (see the xspec manual for details).

To produce a response matrix, DO NOT give your phase-binned spectral file to pcarsp. Instead, extract a normal, un-phase-binned spectrum for the same type of data you gave fasebin (eg., if you ran fasebin on PCA binned mode data, run saextrct on some part of the same binned data and produce a spectrum). Give this un-phase-binned spectrum to pcarsp and make a response matrix from this. Since you are using the same data that you gave to fasebin, the response matrix will be valid for the fasebin spectral file as well. (Good Xenon users only: keep in mind that fasebin, by default, extracts only layer 1. If you used this default behavior, make sure you specify layer 1 only (LR1) when you run pcarsp.)

Subtracting persistent emission

You may subtract the persistent emission (the baseline background) from your data in one easy step, with the FTOOL fbsub:

 fbsub
 Input File[] alldays.pha
 Name of output .pha file[fBsub.pha] alldays_pulsed-only.pha
 Phase minimum[0.0]
 Phase maximum[1.0]

The phase minimum and phase maximum may contain any continuous range of phase space which you feel best represents the unpulsed component for your source. The entire phase range (0.0 to 1.0) may be used in most cases as a good first approximation, since the few phase bins containing the pulsed emission will not effect the baseline much. You may also enter a second phase range to be used in calculating the unpulsed background -- see "fhelp fbsub" for details.

Combining several phase bins into one

You may combine contiguous phase bins into a single spectrum using the FTOOL fbsum:

    fbfsum binstart=5 binstop=8
    Input File[] alldays.pha
    Name of output .pha file[fBfsum.pha] alldays_phase5-8.pha
    Number of phase bins (rows) to be averaged[5] 4

This will create a Type 2 spectral file with a single row representing the combined spectrum for phase bins 5-8. If the last input (number of phase bins) was changed from "4" to "2", the output file would contain two spectra, one for phase bins 5+6, the other for bins 7+8. Leaving out the "binstart=5 binstop=8" parameters on the command line would combine every 4 phase bins in the input file into a single spectrum in the output, resulting in an output file with 5 separate spectra. (The input file contains 20 phase bins.)

Creating a counts-per-phase-bin histogram

To produce a histogram of counts-per-phase-bin, use the FTOOL fbssum:

    fbssum
    Input File[] alldays.pha
    Channels for energy ranges[]

This will sum the counts in all channels for each phase bin, and dump the resulting totals to the screen. Header-style comments at the top of the output define the columns and units, as well as echoing the included channels. You may cut and paste the entire output to a file and plot with any ascii plotting package (eg., QDP, gnuplot, etc.).

Please Note: the resultant histogram covers two full phase cycles, ie., 0.0 to 2.0 in phase space. Thus, if you requested N phased bins when running fasebin, you will have 2N+1 phase bins in your output.

For the syntax on creating histograms for restricted channel ranges, see "fhelp fbssum". BEWARE: the channels are relative to the configuration used, NOT THE ABSOLUTE 0 to 256 CHANNEL RANGE OF THE PCA INSTRUMENT. See the fhelp for further details.